The invention relates to an overload safety device, particularly for industrial robots having a robot arm and a robot tool, preferably arrangable between the robot arm. and the robot tool, with a robot flange and a tool flange, the latter being movable relative to the former.
Working machines, particularly industrial robots often have to move relatively bulky, large or heavy articles at a considerable speed. There is always a risk that, particularly in the case of projecting workpieces, due to the movements extending well beyond the basic dimensions of the industrial robot, contacts or collisions with other workpieces, machines or similar objects in the path of movement will occur. It has therefore become standard practice to fit between the tool and the robot arm an overload safety device of the aforementioned type, which simultaneously constitutes a "predetermined breaking point".
In the case of an industrial robot, the maximum weight of a load which can be moved with said robot at a given input power decreases with increasing lever arm, i.e. with increasing robot arm width. In addition, the robot arm weight reduces the "working load" of the industrial robot. Thus, on the basis of these standpoints, in connection with an overload safety device of the present type there are framework requirements for a minimum axial extension or construction depth and a minimum weight.
In the case of one known overload safety device, an electrical proximity switch is located in the robot flange and is positioned at a certain distance from the tool flange. On modifying the distance between the tool flange and the robot flange, the electrical proximity switch responds and triggers a safety cut-out. This known overload safety device construction is unsatisfactory in connection with the aforementioned requirements concerning a minimum constructional depth and a minimum weight. The electrical proximity switch has a by no means inconsiderable length and contributes significantly to the total weight of the overload safety device. Furthermore, the freedom of movement of the tool flange in the known overload safety device is very limited, because it is constructed around the relatively elongated electrical proximity switch. However, without such a comprehensive construction, the constructional depth of this known overload safety device would be further considerably increased. The tool flange construction embracing the proximity switch can very easily lead to the overload safety device being damaged in the case of certain stresses to the industrial robot, such as those linked with a tilting movement of the tool flange. This leads to a limited possibility of use of the overload safety device.
As electrical switching elements, the proximity switches can also fail as a result of an electrical fault, it generally then being necessary to replace a proximity switch. If it is not the proximity switch which is faulty, the electrical leads can be damaged, particularly in the case ofa continuously moving industrial robot.
The problem of the invention is therefore to provide an overload safety device, which has a minimum construction depth and minimum weight, which can be more widely used and is simultaneously more reliable.